UPS Terms Glossary

Parallel UPS configuration in which several UPS units with equal outputs are parallel connected and share the load. In the event one UPS unit fails, the other units pick up its share without any interruption in the supply of power to the load.

Time during which the UPS can supply the rated load with nominal-quality power while utility power is down. This time depends on the battery and the efficiency of the UPS. Typical backup ranges from five minutes to several hours.

System used for control/monitoring building utilities and systems. It is generally composed of sensors, actuators and programmable controllers connected to a central computer or several computers, equipped with specific software.

The technical description of conductance is the real part of complex admittance. It is a measure of an electrical circuit current response that results when an AC voltage pulse of a known frequency and amplitude is applied. Siemens is the international unit of measure which is sometimes called “MHOS”, which of course is Ohms spelled backward. Conductance is also sometimes referred to as “admittance” or “acceptance”, because it relates the electrical (conductive) efficiency of a circuit. The conductance value is one way to measure the resistive characteristic of any battery or cell. As batteries age and fail, their internal resistance will typically increase because the plate surface can sulfate or shed active material, which adversely affects its ability to perform. This increase in resistance can be observed with declining conductance readings. It is a measure of that decline over time that can be used to calculate the capacity loss in cell or battery as it occurs. This is done without discharging the cell or battery, and the simple rule of thumb is; high conductance is GOOD, low conductance is typically BAD.

Temporary current observed in a network when electrical devices are energized, generally due to the magnetic circuits of the devices. The effect is measured by the currentís maximum peak value and the rms current value it generates.

All alternating current which is not absolutely sinusoidal is made up of a fundamental and a certain number of current harmonics which are the cause of its deformation (distortion) when compared to the theoretical sine-wave. For each current harmonic of order n and an rms value In, there is a voltage harmonic with an rms value Un. If Zsn is the voltage source output impedance for the harmonic of the nth order, then: Un = Zsn x In

Transmission system used on certain devices and offering better performance than the RS232C. It provides a high degree of immunity to interference and is easy to implement, but has not been standardized.

Ratio between the rms value of all harmonics of a non-sinusoidal alternating periodic value and that of the fundamental. This value may also be expressed as a function of the individual distortion of each harmonic Hn = Yn /Y1

Filter used to reduce, if necessary, the overall distortion due to the current harmonics injected into the utility upstream of a UPS by its rectifier-charger. Filtering is superior to that of a traditional filter of the L or C type.

Theorem stating that any non-sinusoidal periodic function (frequency f) may be represented as a sum of terms (series) made up of: n a sinusoidal term with frequency f, called the fundamental frequency, n sinusoidal terms with frequencies that are whole multiples of the fundamental frequency, (harmonics), n a possible DC component where n is a whole number. n = 1 corresponds to the fundamental, n > 1 to the harmonic of the nth order.

Sinusoidal term of the Fourier series expansion of a periodic function. The harmonic (or harmonic component) of the nth order is characterised by: Yn is the rms value of the given harmonic component, w is the angular frequency of the fundamental, related to frequency by : w = 2¼f; phin is the phase angle of the given harmonic component at t = 0.

All alternating current which is not absolutely sinusoidal is made up of a fundamental and a certain number of current harmonics which are the cause of its deformation (distortion) when compared to the theoretical sine-wave. For each current harmonic of order n and an rms value In, there is a voltage harmonic with an rms value Un. If Zsn is the voltage source output impedance for the harmonic of the nth order, then: Un = Zsn x In

Temporary current observed in a network when electrical devices are energized, generally due to the magnetic circuits of the devices. The effect is measured by the currentís maximum peak value and the rms current value it generates.

UPS subassembly that recomposes a sine-wave output (regulated and without breaks) using the DC current supplied by the rectifier-charger or the battery. The primary elements of the inverter are the DC/AC converter, a regulation system and an output filter.

UPS configuration in which the inverter is parallel-mounted to the load supply line and backs up the utility. This configuration offers a substantial cost reduction but is applicable only to low outputs, under 3 kVA, because it results in an interruption lasting up to 10 ms during transfer and does not filter inrush currents.

UPS configuration in which the inverter is in series mounted between the utility and the load. All power drawn by the load passes via the inverter. This is the only configuration used for high outputs.

Load (generally with a switched-mode power supply) generating major harmonic currents. Current wave form is out of phase with the voltage wave form. Ohm’s law is not applicable. It can be used only with each harmonic.

Manually operated series of circuit breakers creating a make before break (preferably) parallel path around the UPS and static switch. Once energized, all load power is supplied through the bypass, and the UPS can be completely de-energized allowing any service activity. Micro-outage (or micro-interruption) Total loss in the supply of power for 10 ms.

Mathematical calculation of the duration of normal operation of a non-reparable device, i.e. for which a MTBF is not possible. The product, expressed in hours, is an indication on the reliability of the device.

Load (generally with a switched-mode power supply) generating major harmonic currents. Current wave form is out of phase with the voltage wave form. Ohm’s law is not applicable. It can be used only with each harmonic.

UPS configuration in which the inverter is parallel-mounted to the load supply line and backs up the utility. This configuration offers a substantial cost reduction but is applicable only to low outputs, under 3 kVA, because it results in an interruption lasting up to 10 ms during transfer and does not filter inrush currents.

UPS configuration in which the inverter is in series mounted between the utility and the load. All power drawn by the load passes via the inverter. This is the only configuration used for high outputs.

Ratio between the rms value of all harmonics of a non-sinusoidal alternating periodic value and that of the fundamental. This value may also be expressed as a function of the individual distortion of each harmonic Hn = Yn /Y1

Filter used to reduce, if necessary, the overall distortion due to the current harmonics injected into the utility upstream of a UPS by its rectifier-charger. Filtering is superior to that of a traditional filter of the L or C type.

Inverter high-frequency chopping technique using a means of regulation enabling rapid modification of pulse widths over a single period, thus making it possible to maintain the inverter output within tolerances even for non-linear loads.

Relative measurement (%) of the internal impedance of an AC generator during harmonic phenomena. This reactance, also called the longitudinal subtransient reactance of the generator, is sometimes identified as X”d. For most common generators, the value ranges between 15 and 20%. It can drop to 12% for optimized systems and to 6% for special devices.

UPS component that draws on the mains the power required to supply the inverter and to float charge or recharge the battery. The alternating input current is rectified and then distributed to the inverter and the battery.

Parallel UPS configuration in which several UPS units with equal outputs are parallel connected and share the load. In the event one UPS unit fails, the other units pick up its share without any interruption in the supply of power to the load.

UPS configuration in which one or several UPS units operate on stand-by, with no load or only a partial load, and can immediately back up a faulty UPS unit by no-break transfer of the load, carried out by a static switch.

Probability that a device will accomplish a required function under given conditions over a given period of time. Rms value of AC current with harmonics The rms value Yrms of a non-sinusoidal alternating current may be determined on the basis of the individual harmonic currents: where Y is the rms value of the fundamental.

Standard defining the communication circuits between devices for synchronous and asynchronous transmissions on the following types of lines: two-wire, four-wire, point-to-point, telephone lines and local links with short cables. Though the standard covers only transmissions over distances up to 15 meters, it is often possible to ensure correct transmission over greater distances using high-quality shielded cable in a reasonably satisfactory electrical environment. Most terminals and devices on the market can implement this transmission standard.

Standard RS232C is sufficient for transmissions in a normal environment. For transmissions in a disturbed environment or over long distances, standard RS422A offers a differential operation option, with a balanced voltage, ensuring far superior performance. What is more, it can be used for multipoint links, with generally up to ten connection points (one sender and up to ten receivers).

This standard is similar to RS422A except that the number of possible links is greater and up to 32 senders may be interconnected to as many receivers. This system is particularly designed for local-area networks.

Installation supplying electrical equipment which may have a direct effect on the safety of users and must therefore remain energised even in the event of a mains failure. In general, characteristics concerning the power supply and conditions for transfer to the safety source for such electrical equipment are covered by applicable regulations.

Power-electronics device that can be used to switch from one source to another without interruption in the supply of power. In a UPS, transfer is from Mains 1 to Mains 2 and back. Transfer without interruption is possible due to the fact that there are no mechanical parts and the ultra-fast switching capabilities of the electronic components.

Relative measurement (%) of the internal impedance of an AC generator during harmonic phenomena. This reactance, also called the longitudinal subtransient reactance of the generator, is sometimes identified as X”d. For most common generators, the value ranges between 15 and 20%. It can drop to 12% for optimized systems and to 6% for special devices.

Thermal runaway occurs in a VRLA battery when the rate of internal heat generation exceeds the rate at which the heat can be dissipated into the environment.It is typically triggered by excessive charge voltage, or high ambient temperatures. As temperature rises, internal current rises, resulting in higher internal temperatures, and a self-sustaining run away cycle. Should this condition continue for an extended period, the VRLA battery temperature could increase until ultimately the cells will dry-out and the container, if plastic, may soften (100°C), rupture and melt (160°C).Thermal runaway is a dangerous condition that can cause damage to property, fire and harm to personnel.

For a given load, it is possible to consider the power supply as a voltage generator, referred to as a Thevenin generator, made up of a perfect voltage Uo generator, in series with an internal impedance Zs: n Uo is the voltage measured across the load terminals, given that the load is to be disconnected (load terminals forming an open circuit), n Zs is the equivalent impedance as seen from the load terminals (again considered an open circuit), obtained by short-circuiting the upstream voltage generator(s).

Relative measurement (%) of the internal impedance of a transformer. This short-circuit impedance is commonly called the short-circuit voltage because it is measured during a short-circuit test (shorted secondary winding subjected to a current set to In). For most common three-phase transformers, this value ranges between 3 and 6%.

Underwriters Laboratories (UL) is a non-governmental, non-profit certification organization in the United States in which not only government authorities are represented, but also consumer groups, “export” services, research, etc. Following certification, a product may bear the UL label.

An electrical device providing an interface between the mains power supply and sensitive loads (computer systems, instrumentation, etc.). The UPS supplies sinusoidal AC power free of disturbances and within strict amplitude and frequency tolerances. It is generally made up of a rectifier/charger and an inverter together with a battery for backup power in the event of a mains failure.

A UPS made up of several parallel-connected UPS units with equal output ratings (P) and each equipped with its battery. If one unit fails, one or several of the others pick up the resulting excess load. If a UPS has a rated output n x P and is made up of n + k units, k is the level of redundancy for the entire set of n + k units.

A UPS made up of several (n) parallel-connected UPS units with equal output ratings (P) and each equipped with its battery, for large loads. The total output is equal to the number of units multiplied by their individual output (n x P). In this configuration, no UPS unit is redundant.

All alternating current which is not absolutely sinusoidal is made up of a fundamental and a certain number of current harmonics which are the cause of its deformation (distortion) when compared to the theoretical sine-wave. For each current harmonic of order n and an rms value In, there is a voltage harmonic with an rms value Un. If Zsn is the voltage source output impedance for the harmonic of the nth order, then: Un = Zsn x In